Method of cathodically descalling and electrode therefor



June 23, 1953 c, cox 2,643,222

METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR Filed March 24,1949 5 Sheets-Sheet l llll I June 23, 1953 G. c. COX

METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR File d March 24,1949 3 Sheets-Sheet 2 IN V EN TOR.

G. C. COX

June 23, 1953 METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFORFiled March 24, 1949 3 Sheets-Sheerv 3 INVENTOR.

Patented June 23, 1953 UNITED STATES PATENT OFFICE METHOD OFCATHODICALLY DESCALING AND ELECTRODE THEREFOR This invention relates toimproved apparatus and methods for electrolytically treatin metalsurfaces such, for example as areas of the side, bottom or deck surfacesof floating marine structures or the inner or outer surfaces of metaltanks, tank cars, etc. More particularly this invention relates to anelectrode structure capable of effectively distributing an electriccurrent at any desired current density up to several hundred amperes persquare foot when using electrolytes such as sea Water or otherelectrolytes of equal or greater conductivity.

This electrode structure can be made to function completely as an anodewith the structure undergoing treatment serving as a coacting cathode;or such a structure can be made to function as a cathode with thestructure under treatment serving as a coacting anode; or a part can bemade to act as an anode and another part as cathode with the adjacentmetal surfaces acting respectively as a coacting cathode and a coactinganode.

An object of this electrode structure is to create a means and methodwhich will efficiently descale or derust a large steel surface at a unitcost lower than other present-day equipment.

Another object is to produce an electrode structure which can be usedwhen electrolytically depositing a protective coating on such surfacesunder low cost controlled conditions.

Another object is to produce an electrode equipment which willeffectively treat a metal surface by the use of an external power sourcethe voltage of which is less than that required to form a destructiveelectric are.

A further object is to produce an electrode equipment the electrodeelements of which galvanically coact with the metal surface undertreatment to produce the required electric current for the operationwithout the use of an external current source.

Another object is to combine any of the above objects as required tomeet a specific treating use.

The above and further objects will be apparent when the followingspecifications are read in conjunction with the accompanying drawingswhere- Figure 1 shows a plan view of a part of a woven mat typeelectrode in which the electrode elements are round rods suitably spacedby inter- Woven cords.

Figure 2 is a section on the line 22 of Figure 1.

Figure 3 is a section on the line 3-3 of Figure 1 and illustrates onemethod of leading current to or from the electrode elements.

Figure 4 is a plan view similar to Figure 1 except that the weaving isintermittently arranged along the electrode elements at desiredintervals so that the elements will be held in position with a minimumof interwoven cords.

Figure 5 is a plan view of a part of a mat type electrode in which theindividual electrode elements are spaced from each other by cords orother non-metallic separators. One or more separators may be used to getany desired spacing between the electrode elements.

Figure 6 is a section of a woven mat type electrode resting on a steelsurface to be treated and shows the use of flattened bars or ribbon typeelectrode elements.

Figure '7 is a sectional view similar to Figure 2 but shows a section ofa mat electrode in an operating position supported on the steel surfaceto be treated, the electrode weaving cords being several diameterssmaller than the round electrode elements.

Figure 8 shows the plan view of a part of a mat type electrode in whichthe electrode elements are held in position by placing sheets of clothor of non-metallic gauze on each side of the elements and sewing thesesheets together between each element. If desired, more than oneelectrode element insert may be placed in the same pocket; or anelectrode element may be omitted from every other pocket or otherwise,as required. An advantage of this arrangement is that new electrodeelements may be inserted into these pocketlike spaces when the old onesbecome useless.

Figure 9 is a cross sectional view along the line 99 of Figure 8,showing the substantially tubular pockets.

Figure 10 is a sectional view similar to Figure 9 except that thereplaceable electrode elements are flattened or ribbon-type bars. Thisfigure shows these insert bars resting on and pressing against one ofthe sheets of porous non-conducting material which, in turn, is restingon and pressing against the steel surface to be treated.

Figure 11 is a sectional view similar to Figure 10 showing a modifiedform of insert in elongated pockets.

Various attempts have been made to produce an electrolytic equipmentwhich can be used for descaling or otherwise treating metal surfacessuch as the steel decks and sides of ships, storage tanks, etc., whichare covered with corrosion products, old paint, films, etc.

Both from a practical consideration of availability without specialpreparation and an economic consideration of cost, the desirableelectrolyte for treating marine structures is sea water. For treatinginland structures, somewhat similar electrolytes may be used. However,the equipments can be adapted to use a wide variety of electrolytes forvarious specific applications.

Tests show that a commercial marine design of a 7,000 ampere moving typegrid electrode made in accordance with applicants co-pending applicationNo. 550,814 of August 23, 1944, now Patent Number 2,476,286, andoperating with a sea water electrolyte required a minimum operatingvoltage of about 50 at the lower descaling current densities and amaximum of 140 volts for the higher current densities. Under normaloperating conditions these secondary arc suppressor electrodes functionperfectly but if one becomes broken and shorted to the main electrode,an arc can be set up between the broken electrode and the work.

An inherent design feature of such an externally powered grid electrodefor rapid descaling is that the total gap between the input electrodeand the work must be maintained at a distance which will safely preventthe formation of destructive arcs. Distances of one to four inches ormore are common in the prior art; the shorter distance can be used withthe arc suppressor electrodes and the longer distance is possiblewithout such electrodes.

In this invention the gaps between the electrode elements and the workto be descaled or otherwise treated are comparatively so small that therequired current density on the work surface can be obtained with a seawater electrolyte by the use of an applied voltage which is Well belowthe zone of transition from spark to arc. Depending on conditions, thistransition from a spark to an are that will maintain itself begins whenthe applied voltage is raised above 25 to 30 volts. As the voltage isfurther increased the arc becomes more penetrating and destructive. Evenwith gap distances between electrode elements and the work surface up toone-fourth of an inch as herein disclosed, tests indicate that operatingvoltages in excess of fourteen are seldom necessary and usually therequired voltages are below seven.

For example, when using normal sea water, one of these mat type gridelectrodes gave a current dissipation when pressed against a steelsurface equivalent to approximately one hundred amperes per square footwith an applied voltage of 2.10 volts. The grid was anodic and the workwas cathodic. This electrode was constructed by weaving inch mild steelrods together with cotton cord of approximately inch in diameter. Thecurrent was fed to these steel elements by the arrangement shown inFigure 1.

A similarly constructed mat electrode using malleable magnesium elementsproduced, under similar conditions, a current density equivalent .toapproximately 25 amperes per square foot even when no external voltagewas applied. With an externally applied voltage of 2.05 volts theequivalent current density on the steel surface in contact with themagnesium mat electrode was more than 200 amperes per square foot.Depending upon the type of scale to be removed a current density notexceeding 100 amperes per square foot is generally suflicient forordinary descaling with these electrodes.

Hence, for certain uses it is found that a magnesium mat type electrodewill operate effectively without the application of an external currentsource. A study of other materials for the elements of these mat typeelectrodes showed that zinc and aluminum alloys give current densitiesgenerally between the values of the above examples. Electrode elementsmade of copper or other commercial metals or alloys may be necessary forspecific applications, such, for example. as anodic descaling or similartreatments.

A study of electrolytes which may be used in addition to sea water andsimilar solutions showed that most sulphate or chloride brines of thealkali or alkaline earth groups would give useful descaling. When usingdilute acid solutions of less than one-half of one percentefi'ectivedescaling has also been obtained. Similarly, these mat typeelectrodes have been found to be highly effective for electrocoating andelectroplating with electrolytes compounded for a specific use.

Reference will now be made to the drawings in .detail, in which similarnumbers refer to similar parts:

In Figure 1, rod type electrode elements I are positioned and held inplace by means of cords of any flexible non-conducting material 2. Whenit is desired to have the rod type elements of about three to ten feetlong these elements may be fed into a loom from each side and are heldby the warp. In this case the cords 2 comprise most of the warp.However, at least one edge of the warp consists of flexible strands of agood conductor such as copper. The combined crosssectional area of theseflexible stranded conductors must be sufiicient to carry the electriccurrent used in the operation, and are shown as flexible conductors 3 inFigures 1 and 3. The ends of these conductors 3 are clamped under theterminal blocks 4 to which is attached through the lugs 5 heavy currentcarrying cables 6 for leading the current to or from the mat typeelectrode. It is observed that such a flexible electric currentconnection may be easily woven on the electrode elements at any one ormore desired 10- cations along their lengths.

When the electrode elements are continuous or more than about ten feetin length, the electrode elements I could be strung in the loom as thewarp and the non-conducting cords 2 could be woven in by the shuttle. Inthis case the hexible stranded wires 3 sould be woven in place whenrequired at suitable intervals along the electrode elements.

Various other methods of making suitable low resistance connections tothe electrode elements may be used. For example, when such a matelectrode with comparatively long electrode elements is fastened inplace against a surface to be treated, the ends of each of the elementscould be clamped directly to one or more terminal lugs 4 as required.When using galvanic rod elements the ends of these rods could beconnected directly to the work. It is often desirable to have a wire ofmalleable aluminum, copper or iron extruded in the center of such rodsso that sufficient mechanical strength and low conductivity will beinsured.

In order to produce a mat electrode with large mesh openings the weavingcords 2 may be spaced along the electrole elements I at intervals whichwill give the desired mesh openings as shown in Figure 4.

Figure 5 illustrates a method of spacing the electrode elements atgreater distances than shown in the previous figures. This isaccomplished by inserting one or more spacing cords 1 between theelements I. Instead of cords, nonconducting bars or rods may be used.This arr'angeinent would effect lower operating current densities thanwith the closely spaced elements and would be useful in electroplatingor electrocoating large surfaces after they are descaled.

In many cases economics will require the use of flattened bars or ribbontype of electrode elements as shown in Figure 6. One example of such ause would be when galvanic or sacrificial anode elements are intended tohave a limited life and cannot be recovered economically after beinginstalled. For this use the ribbon elements 8 could be made of asuitable galvanic metal or alloy and could be designed for a limitedamperehour life.

With electrolytes such as sea water and the like extensive experimenthas demonstrated that, for a given applied voltage less than thatrequired to form and sustain an electric arc, the current output perunit area of one of these mat type grid electrodes increases rapidly asthe distance is decreased from about one-half inch to about onethirty-second inch or less. The arrangement shown in Figure 7illustrates one way in which this may be accomplished. By the use ofcords 2a which are several times smaller than the diameter of theelectrode elements la, the distance between these elements and thesurface of the sheet of steel 9 can be reduced to comparatively smallvalues.

It is thus seen that the various arrangements shown may be defined as amat type of electrode comprising a multiplicity of metallic electrodeelements which are substantially longer in one dimension than the otherand which have means for holding these elements side by side in aflexible relation to each other and substantially parallel, means forsupporting these elements out of contact with the metal surfaceundergoing treatment, and means for electrically connecting theseelements as required.

Another practical method of accomplishing the same thing is illustratedin Figures 8, 9, and 10. Two pieces of fabric Ill and II are heldtogether by stitches l2, as shown. This stitching can be done on anautomatic machine after the rods are assembled in place between thefabric. This procedure would lend itself to the manufacture of long matelectrodes by continuously feeding the fabric from rolls into anautomatic stitcher while at the same time feeding the electrode elementsfrom suitable coils. For smaller mat type grid electrodes in which theelectrode elements are not more than about 10 to 14 feet long it isentirely practical to sew the two pieces of fabric together as shown atI2 and then slide the electrode elements into the individual tube-likejackets. In other words, this arrangement produces a multiplicity ofsubstantially parallel non-conducting porous walled tubular pocketswhich are flexibly interconnected or interlaced along the sides of theirlong dimension in which the metallic electrode element inserts can beheld.

The cords 2 and lid for weaving the electrode elements into mats asshown in Figures 1 to 7 and the cord 01 thread for weaving the fabric l9and H shown in Figures 8 to 10 should ordinarily be porous and highlyabsorbent to water. Loosely twisted cotton cord or loosely woven cottoncloth have given excellent results. For acid electrolytes good resultswere obtained when using a commercial grade of flexible plasticwaterproof window screen for the fabric sheets l0 and II. In general, alower cell resistance and better results are obtainecl when using afabric 6 having water absorbent porous filaments. Obviously the use of awaterproof or absorbent filament will depend on the reaction productsand intended life of the mat.

When using a fabric having either absorbent or waterproof filaments thesize of the mesh or the closeness of the weave should be such that theelectrolyte will freely pass through the mat, also that any gasgenerated at the work surface or electrode surface will easily escapeand not remain as small trapped gas bubbles in the interstices. Theoccurrence of either of those situations causes an undesirable rise inthe electrical resistance of the cell. A felt of high porosity givesgood results as the fabric sheets Ill and II. Other materials of thedesired characteristics may be used, as impregnated fabrics.

When a mat type grid electrode having highly porous fibers is resting ona flat steel surface, for example, the steel deck of a ship, the weightof the electrode elements press the fabric ll against the deck surfacealong the areas immediately under the electrode elements. Now if seawater or other desired electrolyte is sprayed or otherwise poured overthe mat the electrolyte will be quickly absorbed in all the pores andmeshes of the fabric and the internal electrical resistance across thiscell will drop to values approaching those obtained if the cellcomponents were submerged in the same solution. Under these conditionswith a sea water electrolyte, excellent descaling can be obtained whenthe external circuit is properly completed through an external powersupply when using non-galvanic anodes, or direct to the surface undertreatment when suitable galvanic anodes are used.

The materials which have given excellent results as galvanic orself-generating electrode elements are the commercial magnesium alloyscontaining small percentages of aluminum and zinc, and aluminum alloyscontaining a small percentage of zinc. Electrode elements of pure zincare useful in certain applications requiring only moderate currentdensities.

The materials which have given excellent results as anode elements whendriven from an external low voltage power supply are the alloys ofaluminum of commercial cell grade purity. The least expensive grade ofmild steel reinforcing rods have given good results as electrodeelements when driven from an external power supply. Copper or its alloysare sometimes required particularly when used for cathodes.

The use of galvanic anodes with an external power supply will give anextremely high current output for a limited period. This arrangement hasbeen found useful for treating a surface covered with a firmly attachedhard scale.

In general, ordinary round rods or ribbon type electrode elements areused. However, for an electrode having a large current output and ashort life, the electrode elements may be made of strips of perforated,expanded or crimped metal which are held between fabric sheets ill and l1, similar to the procedure described above. Such an arrangement isshown in Figure 11 in which the inserts 13 are held in the elongatedpockets by sewing the fabric sheets Ill and H together at suitabledistances by stitches l2. For heavy current output, the exposed surfaceof these inserts per unit weight is made comparatively large by usingperforated, expanded or 'crimped metal. When very large electrodesareconstructed, these elongated pockets may be made sufficiently wideand sufficiently long to hold a commercial size sheet of expanded,crimped or perforated metal in one pocket. When using the rod or ribbontype elements, a lower current density may be obtained by leaving everyother pocket empty, etc. This action would be similar to that shown inFigure 5. Depending upon the use, these mat type grid electrodes can bemade in sizes ranging from about one square foot to several thousandsquare feet of total eifective area.

The novel features of these mat type electrodes are: (1) rod or wiretype electrode elements are surrounded by a sufficient amount ofnon-conducting fibrous material either in the form of filaments, cords,or fabric to prevent the electrode elements from coming in directcontact with the work under treatment; (2) these electrode elements areheld away .from the work surface a sufficient distance to cause a layerof electrolyte to be retained in the pores and meshes of the cords orfabric between the electrode elements and the work; (3) the combinedpores and meshes of the mat must be sufficient to allow the exhaustedelectrolyte to drain away or be replaced either constantly orintermittently by a fresh solution; (4) the electrode elements can beconstructed from the alloys which form effective galvanic couples withthe work under treatment and therefore act as a self-generating currentsource; (5) the same galvanic type of electrode elements can be operatedas driven electrodes when necessary, therefore the storage of more thanone type of mat electrode element is not essential; (6) the device ishighly flexible in one dimension, is comparatively light in weight andcan be rolled up into a long roll like a carpet for easy storage andhandling; (7) the entire device is simple to manufacture and easy andfoolproof to operate.

It is often desirable to use only one or two of the electrode elementsin a suitable pocket type mesh covering for descaling or otherwisetreating small, narrow or otherwise difficult places.

For descaling the deck of a ship an electrode as shown in Figure 1 wouldbe laid flat down against the steel deck. For rapid cathodic descalingthe cables 6 would be connected to the positive terminal of a lowvoltage power source and the other terminal of the power source would beconnected to the deck. The mat is then sprayed continuously orintermittently with a suitable electrolyte, which may be sea water.After the required period the mat is moved and the scale is eitherscraped off mechanically or hosed off with a pressure hose. Whendesirable, anodic descaling can be carried out with exactly the samearrangement except that in this case the deck is connected to thepositive terminal and the electrode to the negative terminal of thepower source.

Excellent cathodic descaling of such a deck surface can be effectedwithout the use of an external power source by the use of magnesium rodelectrode elements. In this case the cable 6 or its equivalent isconnected directly to the deck.

A similar procedure is used for descaling the vertical sides of a shipor storage tank. The only precautions are that the mat must be heldfirmly against the surface to be treated and in general a greaterquantity of electrolyte must be sprayed or hosed onto the mat. A finemesh mat, having good absorbent properties-is generally preferable forthis work.

For descaling the bottom of a ship a mat with a large open meshconstruction as shown in 'Figure 4 is highly desirable and is heldagainst the bottom while the ship is at anchor or tied at a wharf. Thisopen mesh construction allows free :gas movement and escape which inturn causes a slight stirring of the water in which it is immersed.

Although such electrodes have been found useful for various otherdescaling and coating applications, theabove examples illustrate thegeneral types of equipment and methods of operation of these novelprocedures. However, it is intended that the invention is not to belimited to theapparatus and method illustrated, but is to be broadlyinclusive of any and all equivalents both of method and apparatus suchas fall within the scope of the appended claims.

I claim:

1. A flexible mat adapted to be'placedcontiguous with a surface of aniron or steel structure which is -to be electrolytically treatedcomprising a plurality of substantially parallel slender elongated barsof a metal selected from the group consisting of magnesium, magnesiumbase alloys, aluminum or aluminum base alloys; and flexible meansmechanically interconnecting all of the elongated bars at intervalsalong the sides of their long dimension; said flexible means includingat least two parts one of which parts is a flexible porousnon-conductive fabric in mechanical contact with the coacting surface ofthe bars on at least one side of the mat for spacing said bars from thesurface of said structure at a distance equal to the thickness of thefabric, and the other of which parts is a flexible metallic lowresistance conductor electrically interconnecting the bars and adaptedto be electrically connected to the structure to be treated.

2. A flexible mat as defined in claim 1 in which the flexible conductorinterconnects the bars adjacent the ends thereof which form one end ofthe mat and in which the flexible fabric extends over a limited area ofthe bars located between the flexible conductor and the end of the matopposite to the flexible conductor.

3. A flexible'mat as defined in claim 1 in which said flexible meansconstitutes the only means for interconnecting the bars, whereby the matmaybe rolled up, the bars being semi-rigid.

4. An electrode comprising a plurality of slender rods of a metalselected from the group consisting of magnesium, magnesium base alloys,aluminum or aluminum base alloys; means for holding the rods inessentially parallel relationship comprising cords interwoven with therods substantially at right angles to the rods, said cords beingcomposed of flexible non-conductive flbers; a terminal; and flexible lowresistance means electrically interconnecting the rods and the terminal.

5. A mat electrode for treating contiguous metal surfaces of an iron orsteel structure consisting of a plurality of slender rods of a metalselected from the group consisting of magnesium, magnesium base alloys,aluminum or aluminum base alloys, means for spacing the rods from themetal surfaces and for holding the rods in flexible and essentiallyparallel relationship comprising sheets of fabric respectively extendingover the galvanically coacting area of the rods on both sides of the matand including means mechanically interconnecting the sheets (atintervals in 9 thespaces between the rods, a terminal and flexible lowresistance electrical conducting means interconnecting the rods and theterminal.

6. The device of claim in which the fabric is thinner than the rods.

'7. A mat electrode for treating contiguous metal surfaces of an iron orsteel structure consisting of a plurality of slender rods of magnesium,.means for spacing the'rods from the metal surfaces and for holding therods in flexible and essentially parallel relationship comprising sheetsof fabric respectively extending over the galvanically coacting area ofthe'rods on both sides of the mat and including means mechanicallyinterconnecting thesheets at intervals in the spaces between the rods, aterminal, and flexible low resistance electrical conducting meansinterconnecting the rods and the terminal.

81A mat electrode for treating contiguous metal surfaces of an iron orsteel structure consisting of a plurality of slender rods of a magnesiumbase alloy, means for spacing the rods from the metal surfaces and forholding the rods in flexible and essentially parallel relationshipcomprising sheets of fabric respectively extending over the galvanicallycoacting area of the rods on both sides of the mat and including meansmechanically interconnecting the sheets at intervals in the spacesbetween the rods, a terminal, and flexible low resistance electricalconducting means interconnecting the rods and the terminal.

9. A mat electrode for treating contiguous metal surfaces of an iron orsteel structure consisting of a plurality of slender rods of aluminum,means for spacing the rods from the metal surfaces and for holding therods in flexible and essentially parallel relationship comprising sheetsof fabric respectively extending over the galvanically coacting area ofthe rods on both sides of the mat and including means mechanicallyinterconnecting the sheets at intervals in the spaces between the rods,a terminal, and flexible low resistance electrical conducting meansinterconnecting the rods and the terminal.

10. A mat electrode for treating contiguous metal surfaces of an iron orsteel structure consisting of a plurality of slender rods of an aluminumbase alloy, means for spacing the rods from the metal surfaces and forholding the rods in flexible and essentially parallel relationshipcomprising sheets of fabric respectively extending over the galvanioallycoacting area of the rods on both sides of the matand including meansmechanically interconnecting the sheets at intervals in the spacesbetween the rods, a terminal, and flexible low resistance electricalconducting means interconnecting the rods and the terminal.

11. The method of cathodically descaling the surface of an iron or steelstructure at a current density of at least 25 amperes per square footwhich comprises the steps of: holding one side of a thin flexiblenon-conducting porous electrode separator against the surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium, magnesium basealloys, aluminum or aluminum base alloys; connecting the rods through alow resistance flexible conductor to the said structure; then repeatedlyfilling the voids between the rods and the coacting surface of thestructure with an electrolyte suitable for the specific descal ng 10action and for a sufiicient time to descale the surface.

12. The method of cathodically descaling the surface of an iron or steelstructure at a current density of at least 25 amperes per square footwhich comprises the steps of holding one side of a thin flexiblenon-conducting porous electrode separator against the surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium, magnesium basealloys, aluminum or aluminum base alloys; connecting the rods through alow resistance flexible'conductor to the said structure; then repeatedlyfilling the voids between the rods and the coacting surface of thestructure with a brine-suitable for the specific descaling action andfora sufficient time to descale the surface.

13. The method of cathodically descaling the surfaceof an iron. or steelstructure at a current density of at least 25 amperes per square footwhich comprises the steps of: holding one side of a thin flexiblenon-conducting porous electrode separator against the "surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium, magnesium basealloys, aluminum or aluminum base alloys; connecting the rods through alow resistance flexible conductor to the said structure; then repeatedlyfilling the voids between the rods and the coacting surface of thestructure with an electrolyte consisting substantially of sea water andfor a sufficient time to descale the surface.

14. The method of cathodically descaling the surface of an iron or steelstructure at a current density in excess of 25 amperes per square footwhich comprises the steps of: holding one side of a thin flexiblenon-conducting porous electrode separator against the surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium, magnesium basealloys, aluminum or aluminum base alloys; flexibly connecting the rodsto the said structure through a means for generating an additivepolarity low voltage direct current supplementing the galvanicpotential; then repeatedly filling the voids between the rods and thecoacting surface of the structure with an electrolyte suitable for thespecific descaling action and for a sufificient time to descale thesurface.

15. The method of cathodically descaling the surface of an iron or steelstructure at a current density in excess of 25 amperes per square footwhich comprises the steps of: holding one side of a thin flexiblenon-conducting porous electrode separator against the surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium, magnesium basealloys, aluminum or aluminum base alloys; flexibly connecting the rodsto the said structure through a means for generating an additivepolarity low voltage direct current supplementing the galvanicpotential; then repeatedly filling the voids between the rods and thecoacting surface of the structure with a brine suitable for the 1 1specific descaling action and for a sufiicient time to descale thesurface.

16. The method of cathodica'lly descaling the surface of an iron orsteel structure at a current density in excess of 25 amperes per squarefoot 5 which comprises the steps'of: holding one side of a thin flexiblenon-conducting porous electrode separator against the surface of thestructure under treatment by pressing against the separator with thesides of a multiplicity of slender substantially parallel rods of ametal selected from the group consisting of magnesium,

magnesium base alloys, aluminum or aluminum. base alloys; flexiblyconnectin the rodsto the.

said structure through a means for. generating an additive polarity lowvoltage directcurrentt supplementing thegalvanic potential; then re--peatedly filling the voids between the rods and the coacting surface ofthe structure withanelectrolyte consisting substantially of sea waterand for a sufficient time to descale the surface.

GEORGE CHANDLER COX.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date Craney June 13, 1899 Wisnom Dec. 3, 1907 Jenkins Feb. 20, 1912Payne Oct. 3, 1922 Giffen May 17, 1927 Edelman July 3, 1929 Hesse Sept.17, 1940 Taylor Feb. 17, 1948 T'arr June 29, 1948 Butler Oct. 12, 1948Thomas Feb. 6, 1951.

FOREIGN PATENTS Country Date Great Britain of 1852 Great Britain of 1873Great Britain Aug. 10, 1893 Great Britain of 1899 Great Britain Aug. 22,1930

1. A FLEXIBLE MAT ADAPTED TO BE PLACED CONTIGUOUS WITH A SURFACE OF ANIRON OR STEEL STRUCTURE WHICH IS TO BE ELECTROLYTICALLY TREATEDCOMPRISING A PLURALITY OF SUBSTANTIALLY PARALLEL SLENDER ELONGATED BARSOF A METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, MAGNESIUMBASE ALLOYS, ALUMINUM OR ALUMINUM BASE ALLOYS; AND FLEXIBLE MEANSMECHANICALLY INTERCONNECTING ALL OF THE ELONGATED BARS AT INTERVALSALONG THE SIDES OF THEIR LONG DIMENSION; SAID FLEXIBLE MEANS INCLUDINGAT LEAST TWO PARTS ONE OF WHICH PARTS IS A FLEXIBLE POROUSNON-CONDUCTIVE FABRIC IN MECHANICAL CONTACT WITH THE COACTING SURFACE OFTHE BARS ON AT LEAST ONE SIDE OF THE MAT FOR SPACING SAID BARS FROM THESURFACE OF SAID STRUCTURE AT A DISTANCE EQUAL TO THE THICKNESS OF THEFABRIC, AND THE OTHER OF WHICH PARTS IS A FLEXIBLE METALLIC LOWRESISTANCE CONDUCTOR ELECTRICALLY INTERCONNECTING THE BARS AND ADAPTEDTO BE ELECTRICALLY CONNECTED TO THE STRUCTURE TO BE TREATED.